The use of PTC materials in circuit protection devices for low power applications is well known. These materials find utility as resettable fuses in low power electronic circuits to protect electronic devices. In such use, these PTC materials protect sensitive and expensive electronic components from exposure to harmful, electrical faults. When a fault is experienced by a PTC material, the PTC material heats up and the electrical resistance of the device increases thereby quenching the fault and preventing the fault from continuing in the circuit.
A PTC material may be used on its own as a current limiting device in low-voltage systems where there is very little circuit inductance. In these applications, as the PTC material transitions to its high-electrical-resistance state, the electrical current is almost instantaneously reduced thereby limiting the voltage across the PTC material. In addition, the power absorbed by the PTC material is also drastically reduced. This further limits the heat to which the PTC material itself is exposed.
In higher power systems, however, the electrical current does not drop off quickly because of the presence of inductive reactance. In higher power applications, as the PTC material is exposed to a fault and begins to transition to a highly, electrically resistive state, the PTC material would be exposed to enormous voltages and to enormous internal power dissipations. Energies absorbed could swell up to tens of kilo-joules. At these levels, the host of the PTC material would most likely thermally destruct and possibly even ignite.
The present invention overcomes this and other problems and provides a shunt device for use with a PTC material for high power applications to absorb and dissipate energy resulting from an impressed fault.